Optical cross-connect device with transparency

ABSTRACT

A cross-connect device in an optical network which includes a demultiplexer for demultiplexing an input optical signal by channels; a plurality of arbitrary transmission optical receivers for converting the optical channel signals received from the demultiplexer to electrical signals and for recovering a clock signal and data according to a reference clock signal generated at the transmission rate of the electrical signals; a cross-connect switch for path-routing the electrical signals received from the arbitrary transmission optical receivers; a controller for controlling the path-routing of the cross-connect switch; a plurality of arbitrary transmission optical transmitters for converting the electrical signal received from each output port of the cross-connect switch to an optical signal; and, a multiplexer for multiplexing the optical signals received from the arbitrary transmission optical transmitters onto one stand of optical fiber.

CLAIM OF PRIORITY

[0001] This application claims priority to an application entitled“OPTICAL CROSS-CONNECT DEVICE WITH TRANSPARENCY” filed in the KoreanIndustrial Property Office on Dec. 30, 1999 and assigned Ser. No.99-66948.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to an opticalcommunication system, and in particular, to a cross-connect device withan electrical cross-connect switch built therein.

[0004] 2. Description of the Related Art

[0005] In an optical communication system, a wavelength multiplexing isimplemented to make transmission systems more economical. Across-connect device is installed at an intermediate node between anupper node (i.e., a central base station) and a lower node (i.e., asubscriber). The cross-connect device involves transmission andassignment of channel signals. In addition, the device plays animportant role in optimizing traffic, congestion, and network growth foran optical network as well as improving the network survivability.

[0006] Diverse transmission formats are available in the opticaltransmission system in order to transmit information at different bitrates. The common transmission formats include SDH/SONET (SynchronousDigital Hierarchy/Synchronous Optical Network), FDDI (Fiber DistributedData Interface), ESCON (Enterprise Systems Connectivity), Fiber Channel,Gigabit Ethernet, and ATM (Asynchronous Transfer Mode), wherein eachoperates at 125 Mbps, 155 Mbps, 200 Mbps, 622 Mbps, 1062 Mbps, 1.25Gbps, and 2.5 Gbps, respectively.

[0007]FIG. 1 is a block diagram of a conventional optical cross-connectdevice having an electrical cross-connect switch, and FIG. 2 is a blockdiagram of the conventional transmission optical receiver.

[0008] Referring to FIG. 1, the conventional optical cross-connectdevice is comprised of a demultiplexer (DEMUX) 10 for demultiplexing aninput optical signal into different channels; a plurality of singletransmission optical receivers 20 for converting optical channel signalsreceived from the DEMUX 10 to electrical signals; a cross-connect switch30 for path-routing the electrical signals received from the respectivesingle transmission optical receivers 20; a controller 40 forcontrolling the path routing of the cross-connect switch 30; a pluralityof single transmission optical transmitters 50 for converting theelectrical signals received from each output port of the cross-connectswitch 30 to optical signals; and, a multiplexer (MUX) 60 formultiplexing the optical signals received from the single transmissionoptical transmitters 50 onto a strand of optical fiber.

[0009] Referring to FIG. 2, each of the single transmission opticalreceivers 20 includes an opto-electrical converter 22 for converting aninput optical signal to an electrical signal; an amplifier 24 foramplifying the electrical signal received from the opto-electricalconverter 22; a clock generator 26 for generating a reference clocksignal corresponding to the transmission rate of the input opticalsignal; and, a clock data recovery unit 28 for recovering a clock signaland data from the amplified electrical signal received from theamplifier 24.

[0010] The single transmission optical receiver 20 receives an opticalsignal at a predetermined transmission rate in a single transmissionformat applied to the corresponding optical communication system. Theclock generator 26 outputs a clock signal at a predetermined singlefrequency, and the clock data recovery unit 28 recovers the clock signaland data by shaping the waveform of the electrical signal converted fromthe optical signal within the clock signal cycle.

[0011] As described above, because the conventional opticalcross-connect device includes the single transmission optical receivers20 and the single transmission optical transmitters 50 that only supportone predetermined transmission format and its related transmission rate,the device is unable to operate adaptively to the change in thetransmission format and the transmission rate (sometimes referred to ashaving no transparency). Therefore, the conventional opticalcross-connect device has limitations during the operation if thetransmission format used is changed, or if at least two transmissionformats are employed.

[0012] To overcome the limitations, protocol-free systems have beendeveloped to accommodate optical signals with different transmissionrates. However, such protocol-free systems are confined to the waveformshaping of signals, without detecting the transmission rates of thesignals and recovering clock signals. Accordingly, noise and timingjitter are produced and accumulated through the nodes which in turndeteriorate the transmission quality.

SUMMARY OF THE INVENTION

[0013] It is, therefore, an object of the present invention to providean optical cross-connect device with transparency for accommodatingoptical signals with diverse transmission rates.

[0014] It is another object of the present invention to provide anoptical cross-connect device with transparency for increasingtransmission quality and transmission distance.

[0015] The above objects can be achieved by providing an opticalcross-connect device with transparency in an optical communicationsystem. Accordingly, the optical cross-connect device includes ademultiplexer for demultiplexing an input optical signal into differentchannels; a plurality of arbitrary transmission optical receivers forconverting the optical channel signals received from the demultiplexerto electrical signals and for recovering a clock signal and dataaccording to a reference clock signal generated at the transmission rateof the electrical signals; a cross-connect switch that path-routes theelectrical signals received from the arbitrary transmission opticalreceivers; a controller for controlling the path-routing of thecross-connect switch; a plurality of arbitrary transmission opticaltransmitters for converting the electrical signal received from eachoutput port of the cross-connect switch to an optical signal; and, amultiplexer for multiplexing the optical signals received from thearbitrary transmission optical transmitters onto one stand of opticalfiber.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and other objects, features, and advantages of thepresent invention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

[0017]FIG. 1 is a block diagram of a conventional optical cross-connectdevice;

[0018]FIG. 2 is a block diagram of a conventional single transmissionoptical receiver;

[0019]FIG. 3 is a block diagram of an optical cross-connect deviceaccording to a preferred embodiment of the present invention;

[0020]FIG. 4 is a block diagram of an arbitrary transmission opticalreceiver according to the first preferred embodiment of the presentinvention;

[0021]FIG. 4(a) is a block diagram of the transmission rate detectorshown in FIG. 4;

[0022] FIGS. 4(b) and (c) illustrate two input signal at a different bitrate;

[0023]FIG. 5 is a block diagram of an optical cross-connect deviceaccording to another preferred embodiment of the present invention; and,

[0024]FIG. 6 is a block diagram of an arbitrary transmission opticalreceiver according to the second preferred embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] In the following description, for purposes of explanation ratherthan limitation, specific details are set forth such as the particulararchitecture, interfaces, techniques, etc., in order to provide athorough understanding of the present invention. However, it will beapparent to those skilled in the art that the present invention may bepracticed in other embodiments which depart from these specific details.For the purpose of clarity, detailed descriptions of well-known devices,circuits, and methods are omitted so as not to obscure the descriptionof the present invention with unnecessary detail.

[0026]FIGS. 3 and 4 are simplified block diagrams of an opticalcross-connect device and an arbitrary transmission optical receiver,respectively, according to the preferred embodiment of the presentinvention.

[0027] Referring to FIG. 3, the optical cross-connect device accordingto the first preferred embodiment of the present invention inlcudes aDEMUX 110 for demultiplexing input optical signals into differentchannels; a plurality of arbitrary transmission optical receivers 120for converting optical channel signals received from the DEMUC 110 toelectrical signals and for generating clock signals and data accordingto a reference clock signal generated based on the transmission rate ofthe electrical signals; a cross-connect switch 130 for path-routing theelectrical signals received from the respective arbitrary transmissionoptical receivers 120; a controller 140 for controlling the path routingof the cross-connect switch 130; a plurality of arbitrary transmissionoptical transmitters 150 for converting electrical signals received fromeach output port of the cross-connect switch 130 to optical signals;and, an MUX 160 for multiplexing the optical signals received from therespective arbitrary transmission optical transmitters 150 onto a strandof optical fiber.

[0028] With reference to FIG. 4, each of the arbitrary transmissionoptical receivers 120 includes an opto-electrical converter 122 forconverting the input optical signal to an electrical signal; anamplifier 124 for amplifying the electrical signal; a transmission ratedetector 126 for XOR-gating the amplified electrical signal and adelayed signal resulting from delaying the amplified signal for apredetermined time, and for detecting the transmission rate of the inputsignal based on the XOR-gated signal; a reference clock generator 127for generating the reference clock signal according to the detectedtransmission rate; and, a clock data recovery unit 128 for recovering aclock signal and data from the amplified signal received from thetransmission rate detector 126 according to the reference clock signalgenerated by the reference block generator 127.

[0029]FIG. 4(a) is a simplified block diagram of the transmission ratedetector 126 shown in FIG. 4, and FIGS. 4(b) and 4(c) shows signalsoutputted from function blocks, for describing the operation of thetransmission rate detector unit shown in FIG. 4. Referring to FIG. 4(a),the transmission rate detector 126 includes an identification signalgenerator 340 a for delaying an input signal for a predetermined period,comparing the original signal with the delayed signal period by period,and generating a sensing signal, and a transmission rate deriving unit340 b for determining a bit rate of the received signal from a voltagelevel obtained by low-pass-filtering the identification signal. Theidentification signal generator 340 a includes a buffer 341 forduplicating an input signal into two signals equal to the input signal,a delay 342 for delaying one of the buffer outputs by a predeterminedtime, and an operator 343 for performing the exclusive OR(XOR) operationupon the delayed signal and the original input signal, and generating abit rate identification signal.

[0030] With reference to FIG. 4(b), the delay 342 generates a signal (b)delayed from an input signal (a) by a predetermined time D, for theinput of the signal (a) with pulse period 2T. The operator 343 generatesa sensing signal (c) by XOR-gating the input signal (a) with the delayedsignal (b). The sensing signal (c) has a plurality of pulses with highlevel periods presented at the same intervals as D. FIG. 4(c)illustrates an input signal(a) at a different bit rate from that of theinput signal (a) shown in FIG. 4(b). In comparison between FIGS. 4(b)and 4(c), when the sensing signals are generated using input signalsreceived for the same time period, the pulses of the sensing signal(c)are a few times more than those of the sensing signal (c). The pulsenumbers of the sensing signals are different due to the different bitrates of the input signals; thus, the difference between the pulsenumbers is proportional to the difference between the bit rates.Therefore, the transmission rate can be detected by checking the numberof pulses of a sensing signal generated for a predetermined time. Formore details of the operation and configuration of the arbitrarytransmission optical receiver 120, see U.S. patent application Ser. No.09/484,061 filed on Jan. 18, 2000 and U.S. patent application Ser. No.09/621,009 filed on Jul. 20, 2000 by the present applicant. Thus, thedescription of the transmission rate detector is incorporated byreference.

[0031] In the embodiment of the present invention, the transmission ratedetector 126 generates a sensing signal by comparing the delayed signalwith the amplified signal in time and determines the transmission ratebased on a voltage level resulting from low-pass filtering the sensingsignal. That is, the transmission rate detector 126 detects thetransmission rate of the input signal based on the voltage levelobtained by XOR-gating the delayed signal and the amplified signal, thenlow pass filtering the XOR-gated signal.

[0032] The reference clock generator 127 includes a plurality ofoscillators for generating clock signals at different frequencies.Accordingly, the reference clock generator 127 selectively operates oneof the oscillators to generate a reference clock signal corresponding tothe detected transmission rate.

[0033] The clock data recovery unit 128 is a programmable circuit forsubjecting the received electrical signal for reshaping, regenerating,and retiming of an input signal according to the reference clock signalreceived from the reference clock generator 127.

[0034]FIGS. 5 and 6 are respective block diagrams of an opticalcross-connect device and an arbitrary transmission optical receiveraccording to another preferred embodiment of the present invention.

[0035] With reference to FIG. 5, the optical cross-connect deviceaccording to the second preferred embodiment of the present inventionincludes a DEMUX 110 for demultiplexing input optical signals intodifferent channels; a plurality of arbitrary transmission opticalreceivers 220 for outputting a transmission rate monitoring signal tothe controller 240, by converting optical channel signals received fromthe DEMUX 110 to electrical signals, and for recovering clock signalsand data according to a reference clock signal generated from thereference clock generator 226 (will be explained later with reference toFIG. 6) upon receipt of a transmission rate change signal from thecontroller 240; a cross-connect switch 130 for path-routing theelectrical signals received from the arbitrary transmission opticalreceivers 220; a controller 240 for controlling the path routing of thecross-connect switch 130, determining the transmission rate from thetransmission rate monitoring signal, and feeding the transmission ratechange signal to the arbitrary transmission optical receivers 220 and aplurality of arbitrary transmission optical transmitters 250; theplurality of arbitrary transmission optical transmitters 250 forconverting electrical signals received from each output port of thecross-connect switch 130 to optical signals; and, a MUX 160 formultiplexing the optical signals received from the arbitrarytransmission optical transmitters 250 onto a strand of optical fiber.

[0036] The controller 240 has a decider/converter 242 for generating atransmission speed sensing signal by comparing the electrical signalreceived from the arbitrary transmission optical receivers 220 with thesignal resulting from delaying the electrical signal in time, and fordetermining the transmission rate based on the voltage level obtained bylow-pass filtering the sensing signal.

[0037] Referring to FIG. 6, the components of each arbitrarytransmission optical receivers 220 include an opto-electrical converter222 for converting the input optical signal to an electrical signal; anamplifier 224 for amplifying the electrical signal; a reference clockgenerator 226 for generating the reference clock signal according to thetransmission rate change received from the controller 240; and, a clockdata recovery unit 228 for recovering the clock signal and data from theamplified signal received from the amplifier 224 according to thereference clock signal from the reference clock generator 225. Incontrast to the first embodiment, the arbitrary transmission opticalreceiver 220 according to the second embodiment differs in that it doesnot have an interior control means such as the transmission ratedetector, and generates the reference clock signal and recovers theclock signal and data based on the transmission rate informationreceived from the controller 240.

[0038] The reference clock generator 226 includes a plurality ofoscillators for generating clock signals at different frequencies. Thereference clock generator 226 selectively operates one of theoscillators to generate a reference clock signal corresponding to thetransmission rate determined by the controller 240.

[0039] The clock data recovery unit 228 is a programmable circuit forsubjecting the received electrical signal to reshaping, regenerating,and retiming the input signal according to the reference clock signalreceived from the reference clock generator 226.

[0040] As described above, the optical cross-connect device of thepresent invention can ensure transparency, i.e., flexibility, because itaccommodates signals of diverse transmission formats and relatedtransmission rates. Furthermore, a reference clock signal is generatedby detecting a transmission rate, so that noise and timing jitter arereduced and transmission quality and transmission distance are enhanced.

[0041] While the invention has been shown and described with referenceto a certain preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and the scope of theinvention as defined by the appended claims.

What is claimed is:
 1. An optical cross-connect device in an opticalcommunication system, comprising: a demultiplexer for demultiplexing aninput optical signal into different channels; a plurality of opticalreceivers for converting the demultiplexed optical signals received tothe corresponding electrical signals, and for recovering a clock signaland data according to a reference clock signal that is generated basedon a transmission rate of the electrical signals; a cross-connect switchfor path-routing the electrical signals received from the opticalreceivers; a controller for controlling the path-routing of thecross-connect switch; a plurality of transmitters for converting theelectrical signal received from each output port of the cross-connectswitch to an optical signal; and, a multiplexer for multiplexing theoptical signals received from the optical transmitters onto one stand ofoptical fiber.
 2. The optical device of claim 1 , wherein each of theoptical receivers comprises: an opto-electrical converter for convertingthe input optical signal to an electrical signal; an amplifier foramplifying the converted electrical signal; a transmission rate detectorfor XOR-gating the amplified electrical signal and a signal resultingfrom delaying the amplified electrical signal for a predetermined timeand for detecting the transmission rate of the received electricalsignal from the XOR-gated signal; a reference clock generator forgenerating the reference clock signal according to the detectedtransmission rate; and, a clock data recovery unit recovering the clocksignal and data from the electrical signal received from thetransmission rate detector based on the reference clock signal.
 3. Theoptical device of claim 2 , wherein the transmission rate detectorgenerates a sensing signal by comparing the electrical signal with thedelayed signal in time, and determines the transmission rate based on avoltage level obtained by low-pass filtering the sensing signal.
 4. Theoptical device of claim 2 , wherein the reference clock generatorincludes a plurality of oscillators for generating clock signals atdifferent frequencies.
 5. The optical device of claim 2 , wherein thetransmission rate detector comprises: a buffer for receiving theamplified electrical signal; a delay for delaying the amplified signalfor the predetermined time; and, an operator for XOR-gating the delayedsignal with the buffered signal for a prescribed time period.
 6. Theoptical of claim 5 , further comprising: a filter for filtering theXOR-gated signal; a converter for converting the filtered signal to adigital signal; and, a deriving unit for generator the a differenttransmission rate based on the pulses of the converted digital signal.7. An optical cross-connect device in an optical communication system,comprising: a demultiplexer for demultiplexing an input optical signalinto different channels; a plurality of optical receivers for outputtinga transmission rate monitoring signal by converting the demultiplexedsignals received from the demultiplexer to electrical signals, and forrecovering a clock signal and data according to a reference clock signalgenerated upon the receipt of a transmission rate change signal; across-connect switch for path-routing the electrical signals receivedfrom the arbitrary transmission optical receivers; a controller forcontrolling the path-routing of the cross-connect switch, determining atransmission rate from the transmission rate monitoring signal, andfeeding the transmission rate change signal to the arbitrarytransmission optical transmitters; a plurality of optical transmittersfor converting the electrical signal received from each output port ofthe cross-connect switch to an optical signal; and, a multiplexer formultiplexing the optical signals received from the optical transmittersonto one stand of optical fiber.
 8. The optical device of claim 7 ,wherein each of the optical receivers comprises: an opto-electricalconverter for converting the input optical signal to an electricalsignal; an amplifier for amplifying the electrical signal; a referenceclock generator for generating the reference clock signal according tothe transmission rate change signal received from the controller; and, aclock data recovery unit for receiving the electrical signal andrecovering a clock signal and data from the electrical signal based onthe reference clock signal.
 9. The optical device of claim 7 , whereinthe controller includes a decider for generating a sensing signal bycomparing the electrical signal received from the optical receivers witha signal resulting from delaying the electrical signal for apredetermined time, and for determining the transmission rate based onthe voltage level obtained by low-pass filtering the sensing signal. 10.The optical device of claim 8 , wherein the reference clock generatorincludes a plurality of oscillators for generating clock signals atdifferent frequencies.